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VOLUME 84, NUMBER 7 P H Y S I C A L R E V I E W L E T T E R S 14 FEBRUARY 2000 Coulomb Gap: How a Metal Film Becomes an Insulator
 

Summary: VOLUME 84, NUMBER 7 P H Y S I C A L R E V I E W L E T T E R S 14 FEBRUARY 2000
Coulomb Gap: How a Metal Film Becomes an Insulator
V. Yu. Butko,* J. F. DiTusa, and P. W. Adams
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70806
(Received 10 September 1999)
Electron tunneling measurements of the density of states (DOS) in ultrathin Be films reveal that a
correlation gap mediates their insulating behavior. In films with sheet resistance R , 5000 V the cor-
relation singularity appears as the usual perturbative ln V zero bias anomaly (ZBA) in the DOS. As
R is increased further, however, the ZBA grows and begins to dominate the DOS spectrum. This evo-
lution continues until a nonperturbative jVj Efros-Shklovskii Coulomb gap spectrum finally emerges in
the highest R films. Transport measurements of films which display this gap are well described by a
universal variable range hopping law R T h 2e2
exp T0 T 1 2
.
PACS numbers: 71.30.+h, 72.15.Rn, 73.40.Gk
It has been known for some time now that 2D is the
lower critical dimension for disordered transport and that
even a noninteracting 2D electron gas will be localized in
the presence of arbitrarily small disorder in the thermo-
dynamic limit [1,2]. When these systems are probed at a

  

Source: Adams, Philip W. - Department of Physics and Astronomy, Louisiana State University

 

Collections: Materials Science